1. Field of Invention
The invention relates to a sheet feeder, for use in image forming apparatuses, such as copying machines, printers, and facsimile machines. In particular, the invention relates to a sheet feeder that prevents damages or malfunction of a pick-up roller and a drive system of the sheet feeder by restricting load torque applied when mounted sheets run out.
2. Description of Related Art
As disclosed in, for example, Japanese Laid-Open Patent Publication No. 1-291965, a known sheet feeder for use in, for example, facsimile machines feeds sheets with a pick-up roller by making the pick-up roller contact a stack of a plurality of the sheets and rotating the pick-up roller. Such sheet feeder generally includes a sheet mounting plate that mounts sheets thereon, a pick-up roller disposed so as to face the sheet mounting plate for feeding the sheets mounted on the sheet mounting plate in a sheet feeding direction, an urging member that urges the sheet mounting plate or the pick-up roller in such a direction that the sheet mounting plate and the pick-up roller contact each other, a motor that produces a rotating force, and a plurality of gears that transmit the rotation force of the motor to the pick-up roller. In the above-described known sheet feeder, the pick-up roller contacts the sheets on the sheet mounting plate with an urging force of the urging member. As the rotation of the motor is transmitted to the pick-up roller through the plurality of the gears, the pick-up roller rotates to feed the sheets.
In the above-described known sheet feeder, when the sheets on the sheet mounting plate run out, the pick-up roller contacts the sheet mounting plate with an urging force of the urging member. As the pick-up roller is rotated in this condition, an excessive load is applied to the pick-up roller. Due to the application of the excessive load, motor malfunction that causes unfavorable noises and damages of the sheet feeder may occur.